Direct transfer of the human cystic fibrosis transmembrane conductance regulator (CFTR) gene into human respiratory epithelium with a recombinant virus may correct the severe pulmonary symptoms of cystic fibrosis (CF). Adenovirus (Ad).CFTR recombinant viruses are currently considered promising for use in CF gene therapy. These viruses are deleted in the E1 region of the genome to render them replication-defective and some versions are also deleted in the E3 region to accommodate the CFTR expression cassette in the E1 region. The E3 region of the Ad genome is thoughts to play an important role in helping the virus to evade immunosurveillance and thus persist, by preventing cytolysis by cytotoxic T lymphocytes (CTL) and tumor necrosis factor (TNF) of infected cells. Very little is known about the biology of Ad.CFTR viruses in general, and the specific effects of the lack of expression of the E3 region on, e.g., persistence of the Ad.CFTR viruses, are completely obscure. We hypothesize that E1-deleted replication-defective Ad can induce CTL responses which shorten viral persistence in the infected animal host, and that the E3 region will determine the extent of these biological consequences of such virus infections. Because the normal mechanisms regulating viral persistence are not operative in the immunodeficient host, persistence of E1-deleted viruses (including an Ad.CFTR virus, Ad.CB-CFTR which has E1- and E3-deletions) will be analyzed under immunodeficient and immunocompetent conditions in the cotton rat lung model, using standard methods (RT-PCR, DNA-PCR, Northern blot, Western blot, RNA and DNA in situ hybridization, immunocytochemical techniques and infectious virus titration) to detect viral genome expression (viral gene transcripts, viral proteins and infectious virus) and to detect persistent viral DNA. CTL responses of animal hosts inoculated with E1- and E3-deleted (Ad.E1dl.E3dl) viruses or with viruses deleted only in the E1 region (Ad.E1dl.E3+) will be compared. Assays of the responses of CTL from immunized animals against target cells infected with Ad.E1dl.E3dl (including Ad.CB-CFTR), Ad.E1dl.E3+ and Wt-Ad will reveal the nature of Ad-CTL immunity in the context of CF therapy. Information on the persistence and immunogenicity of E1-deleted viruses will contribute to the design of an optimal Ad.CFTR construct for gene therapy of CF.